JP5828641B2 - Sublimation type image forming apparatus - Google Patents

Description

  The present invention relates to an error diffusion method suitable for a sublimation type image forming apparatus.

2. Description of the Related Art With recent advances in image input devices such as digital cameras, digital video cameras, and scanners, sublimation type image forming devices have attracted attention as image forming devices for printing out images input to image input devices. .
In general, sublimation type image forming apparatuses use thermal paper as printing paper and convey the paper in the sub-scanning direction while selectively driving a plurality of heating elements (recording heads) arranged in the main scanning direction. . As a result, the sublimation dye ink applied to the ink ribbon is transferred onto the printing paper, which is thermal paper, and a dot-line image is formed on the printing paper.

In recent years, there has been an increasing need for a so-called photobook printing format, in which a large number of stored photographs are printed and output one by one, and are printed and booked together for each event. This photo book printing is attracting attention as a new usage of the sublimation type image forming apparatus.
Photo books are often printed for distribution purposes, and users demand high print quality. In the future, higher quality finishes such as higher gradation and higher resolution are expected.
Conventionally, among halftone techniques for converting input image data into image data that can be output by an image forming apparatus, there is an error diffusion method as a method for generating a halftone image with high gradation.

JP-A-10-200742

  However, when the error diffusion method is used in the sublimation type image forming apparatus, there are the following problems.

Usually, in a sublimation type image forming apparatus, even when the gradation value of image data is 0, it is converted into dot data having a pulse value of about several tens of pulses. A pulse value of about several tens of pulses is called a minimum transfer pulse. In the sublimation type image forming apparatus, below the minimum transfer pulse value, the ink or paper medium is a very unstable region, and transfer defects, wrinkles, blurring, foil breakage, etc. are likely to occur. Therefore, it is necessary to control the output value so as not to be less than the minimum transfer pulse value as much as possible to reduce printing in an unstable region. Further, the unstable region varies depending on the temperature of the image forming apparatus and the recording head. When the temperature of the image forming apparatus and recording head is high, the minimum transfer pulse value is lowered, while when the temperature is low, the minimum transfer pulse value is increased to control the steep writing in the paper feed direction. ing. However, when the error diffusion method is performed on the input image data, there is a possibility that the output value is converted to the minimum transfer pulse value or less. In this case, the image quality is significantly deteriorated such as fading of colors and non-transferring. (Figure 2)
On the other hand, Patent Document 1 discloses an error diffusion method for selecting an optimum diffusion coefficient for each gradation value of input image data.

However, in the sublimation image forming apparatus, since the ink dispersion characteristics vary depending on the temperature, the correlation with the gradation value is low, and it is difficult to obtain the effect of the error diffusion method.
The present invention has been made in view of the above problems, and an object of the present invention is to realize high-quality image quality using an appropriate error diffusion method in a sublimation type image forming apparatus.

  In order to solve the above-described problems, the present invention provides a sublimation-type image forming apparatus that performs printing using a recording head, a head temperature measuring unit that measures the temperature of the recording head, and a temperature of the recording head, A range setting means for setting a range of image data that can be stably printed by the image forming apparatus; an error diffusion processing means for quantizing the input image data by an error diffusion method; and the error based on the range. Control means for controlling the result of the diffusion processing means.

  High-quality image quality can be realized by using an appropriate error diffusion method in the sublimation type image forming apparatus.

Block diagram showing system configuration of sublimation image forming apparatus Conceptual diagram showing problems of error diffusion method in sublimation type image forming apparatus Sequence diagram showing processing of CPU and head control ASIC and correlation of processing in embodiment Block diagram showing error diffusion processing in Embodiment 1 Block diagram showing error diffusion processing in Embodiment 2 Block diagram showing error diffusion processing in Embodiment 3 The figure which shows the look-up table which hold | maintains the error diffusion coefficient and coefficient in an Example The figure which shows the look-up table which hold | maintains the error diffusion coefficient group and coefficient group in an Example The figure which shows the diffusion coefficient table holding the error diffusion coefficient group in an Example Conceptual diagram showing from image data reading to printing processing in a sublimation type forming apparatus Block diagram showing the overall configuration of image processing in a sublimation image forming apparatus Sequence diagram showing processing of CPU and head control ASIC and correlation of processing in sublimation type image forming apparatus Conceptual diagram showing temperature correction processing in a sublimation type image forming apparatus Conceptual diagram showing a look-up table storing an effective pulse range used for temperature correction processing in a sublimation type image forming apparatus Conceptual diagram showing a look-up table storing pulse start points used for temperature correction processing in a sublimation type image forming apparatus Block diagram showing error diffusion processing in a sublimation type image forming apparatus Block diagram showing error diffusion processing The figure which shows the diffusion coefficient value of the error diffusion process in a sublimation type image forming apparatus The figure which shows the look-up table which hold | maintains the error diffusion coefficient and coefficient in a sublimation type image forming apparatus

Hereinafter, the present invention will be described in detail based on preferred embodiments with reference to the accompanying drawings.
First, the configuration and operation of the recording head and the head control ASIC in the sublimation type image forming apparatus according to the present embodiment will be described with reference to FIG.

FIG. 1 is a block diagram showing an overall configuration for printing print data in an image forming apparatus. The CPU 4 manages system control and arithmetic processing of the image forming apparatus. The image processing unit 5 processes image data received from a camera or the like or image data acquired from an SD card. The image processing unit 5 performs various kinds of image processing such as decompression on the acquired image data to create image data for printing.
The FLASHROM 9 stores a system control program for the image forming apparatus. The SDRAM 10 is used for temporary storage of image data and data processing work. The SD card 11 is a recording medium for storing data files.

  The card connector 12 is a connector for attaching the SD card 11 to the image forming apparatus. The LCD 13 displays captured images and operation menus. The LCD driver 14 is a driver that drives the LCD. The communication control unit 6 controls communication with a device such as a camera to be connected. The operation unit 7 is input by the user. The head control ASIC 3 converts the image data output from the image processing unit 5 into an electrical signal and outputs the electrical signal to the recording head 2. Then, the recording head 2 converts the electric signal into heat energy, and performs recording on photographic paper (not shown). The head temperature sensor 8 measures the temperature of the recording head. The environmental temperature sensor 1 measures the ambient environmental temperature. The ink ribbon remaining amount meter 15 is used for detecting the remaining amount of the ribbon.

The configuration of FIG. 1 is a general system configuration of a sublimation type image forming apparatus.
FIG. 10 is a conceptual diagram when image data is printed in the sublimation image forming apparatus. The SD card 101, the CPU 102, the head control ASIC 103, and the recording head 104 in FIG. 10 correspond to the SD card 11 and the CPU 4 in FIG. The CPU 102 performs processing such as correction on the input image data read from the SD card 101 and sends the corrected data to the head control ASIC 103. After receiving the corrected data, the head control ASIC 103 performs further correction and converts it into an energization pattern to be sent to the recording head 104. The recording head 104 that has received the energization pattern is energized and generates heat, and the ink 105 is transferred to the photographic paper 106 to perform the printing process.

  As described above, image processing such as correction of input image data is performed in two stages by the CPU 102 and the head control ASIC 103. The image processing method for input image data in the sublimation image forming apparatus will be described in more detail with reference to FIG. The JPEG decompression 111 to various corrections 114 are performed by the CPU 102 in FIG. 10, and the γ correction 115 to the dot data generation 119 are performed by the head control ASIC 103.

First, when JPEG format image data is received from a card medium (not shown), the JPEG decompression unit 111 performs JPEG decompression processing.
The expanded image data has color information including a color difference signal YUV that represents a color by three pieces of information of a luminance signal Y, a blue color difference signal U, and a red color difference signal V. The color conversion 112 converts the image data composed of the YUV signal into YMC image data that can be printed by the sublimation type image forming apparatus. The YMC image data is data representing yellow (Y), magenta (M), and cyan (C).
The resizing process 112 performs a resizing process on the converted image data of each YMC. As the resizing rate, a value input by a user from a user interface (not shown) or the like is used. Next, various corrections 114 including red-eye, face detection, scene discrimination, and the like are performed.

Subsequently, the γ correction 115 converts the gradation value indicated by the CMY image data into a pulse value. A γ table is used for the conversion. Here, in addition to adjusting the gradation of the image data in accordance with the heat generation characteristics of the recording head 104, the following processing is performed so as to ensure the same hue according to the temperature of the recording head 104 and the ambient environmental temperature. Is going.
The γ correction 115 process will be described in detail with reference to FIGS. 13, 14, and 15. FIG. 13 shows an outline of the γ correction 115. Normally, in a sublimation type image forming apparatus, even when the gradation value of image data is 0, it is converted into dot data having a pulse value of about several tens of pulses. This is to reduce printing in an unstable region in the sublimation type image forming apparatus by continuously energizing the recording head.

  In this embodiment, a pulse value corresponding to a gradation value of 0 in the image data is referred to as a minimum transfer pulse Sp. The minimum transfer pulse Sp is a lower limit value of a region where the sublimation image forming apparatus according to the present exemplary embodiment can stably print and output, and depends on the temperature of the recording head and the environment. Γ correction is performed so that the pulse value to be transferred does not fall below the minimum transfer pulse Sp as much as possible. The minimum transfer pulse Sp is set using a lookup table shown in FIG. The minimum transfer pulse Sp is determined corresponding to the combination of the environmental temperature and the head temperature.

When converting 256 gradation image data into 1024 gradation dot data, first, the γ table of FIG. 13A is read from the FLASH ROM 9 of FIG. 1, and the γ table is normalized starting from the lowest transfer pulse Sp. To do. The γ table in FIG. 13B shows the heat generation characteristics of the recording head obtained by normalizing FIG. At this time, the transfer pulse effective range Vp, which is a pulse range that can actually be stably transferred, is set so that the sum of the minimum transfer pulse Sp and the maximum number of pulses is 1024. That is, the transfer pulse effective range Vp is a range of image data that can be stably printed by the sublimation type image forming apparatus in this embodiment. In this example, the transfer pulse effective range Vp is calculated in advance and stored in a lookup table as shown in FIG. The transfer pulse effective range Vp is set using a lookup table shown in FIG. The transfer pulse effective time Vp is determined corresponding to the combination of the environmental temperature and the head temperature, as in the case of the minimum transfer pulse Sp.
Note that the lookup tables shown in FIGS. 14 and 15 are stored in advance in the FLASH ROM 9 of FIG.

As described above, the γ correction 115 determines the transfer pulse effective range Vp and the minimum transfer pulse Sp based on the results measured by the environmental temperature sensor 1 and the head temperature sensor 8 in FIG. 1, and the temperature of the sublimation image forming apparatus. A γ table shown in FIG. 13B suitable for the conditions is generated and γ correction is performed.
After the γ correction 115, the thermal history correction 116 estimates the temperature rise from the past energization history and corrects for each line. In the sublimation type image forming apparatus, since the substrate and the like store heat by energizing the recording head 104, the energization time to the recording head is corrected and the heat generation temperature is made constant according to the heat storage phenomenon.
Up to the various corrections 114 are performed in units of pixels or planes, but the γ correction 115 and the thermal history correction 116 are processed in units of lines. In the present embodiment, data up to various corrections 114 is temporarily stored in the SDRAM 10 of FIG. 1, and data is sent for each line in response to a request from the head control ASIC 3.
The image data output from the thermal history correction 116 is subjected to edge enhancement processing at the edge enhancement 117, and error diffusion processing is performed at the error diffusion processing 118. The error diffusion process 118 will be described in detail with reference to FIGS. The edge enhancement process 117 and the error diffusion process 118 are performed on a pixel basis.

  In FIG. 16, the image data received from the edge enhancement 117 is input image data, and the output to the dot data generation 119 is output image data.

  First, the adder 164 adds the quantization error diffused from surrounding pixels to the target pixel to the input image data. The quantizer 161 quantizes the image data to which the quantization error has been added. The subtractor 162 calculates a difference between the input value and the output value of the quantizer 161 and derives a quantization error. The diffusion filter 163 multiplies the quantization error by the diffusion coefficient shown in FIG. FIG. 18A has diffusion coefficients C1, C2, C3, and C4 corresponding to pixels around the pixel of interest 181. It has a role of diffusing the derived quantization error of the target pixel to surrounding pixels. Actually, the coefficients are set as shown in FIG.

Further, the diffusion coefficient used in the error diffusion processing in the present embodiment may be configured to be selected from a plurality of coefficients held in the lookup table according to the gradation value of the input image data. FIG. 17 shows a part of the configuration of error diffusion processing. Since the quantizer 171, the subtractor 172, the diffusion coefficient filter 173, and the adder 174 in FIG. 17 have the same configuration as that in FIG. 16, description thereof is omitted. In the coefficient LUT 175, a diffusion coefficient group Cb that is a combination of the diffusion coefficients C1, C2, C3, and C4 as shown in FIG. 19A is held for each gradation value as shown in FIG. 19B. . In an error diffusion process using only one diffusion coefficient filter, an error distribution ratio to the neighboring pixels is always constant, and thus a noise pattern may occur on the output image. Therefore, a plurality of diffusion coefficient filters are prepared and selected for each gradation value to diffuse the error, so that the distribution ratio of the error to the surrounding pixels in the target pixel does not become constant. By selecting the diffusion coefficient group Cb corresponding to the gradation value of the input image data, it is possible to obtain a better error diffusion effect. The error diffusion 118 has been described above.
Finally, dot data generation 119 is performed, and an energization pattern for the recording head 2 in FIG. 1 is created.

  The above description of the processes 111 to 119 is applied to an actual printing sequence, and will be described with reference to FIG. Here, the flow from step S121 to step S140 will be described using a process for Y image data. Since the processing from step S121 to step S140 is performed on the Y, M, C surface and the protective film surface, the processing is repeated four times for one printed matter.

  FIG. 12 is a sequence diagram showing the correlation between the processing of the CPU 4 and the processing of the head control ASIC 3 in the sublimation type image forming apparatus and each processing. As described above, the image processing is performed in two stages of the CPU 4 and the head control ASIC 3. Steps S121 to S124 are the same as steps 111 to 114 in FIG. In step S125, the Y plane image data is once written in the SDRAM 10 of FIG. In step S126, the environmental temperature sensor 1 measures the environmental temperature, and in step S127, the head temperature sensor 8 measures the temperature of the recording head 2.

  Thereafter, in step S128 and step S129, the minimum transfer pulse Sp and the transfer pulse effective range Vp are derived. Based on the minimum transfer pulse Sp and the transfer pulse effective range Vp, a one-dimensional γ table is generated in step S130 and written to the SDRAM 10. In step S131, the γ table written in the SDRAM 10 is transferred from the CPU to the head control ASIC, and in step S132, writing is performed in a register (not shown) in the head control ASIC3. In step S133, the Y plane data is transferred from the CPU 4 to the head control ASIC 3, and sequentially processed by the head control ASIC 3. Steps S134 to S138 are the same as steps 115 to 119 in FIG.

  Finally, in step S139, an energization request is issued from the CPU to the head control ASIC. In step S140, energization of the head is started. In step S141, the CPU starts processing of the next M surface. Since the above processing is performed on the Y, M, C surface and the protective film surface, it is repeated a total of four times for one printed matter.

Example 1
Hereinafter, one embodiment will be described in detail with reference to FIGS. 3, 4, 7, 8, and 9. Detailed description of the same configuration as that of the above-described embodiment is omitted.
FIG. 3 is a sequence diagram illustrating the correlation between the processing of the CPU 4 and the processing of the head control ASIC 3 of the sublimation image forming apparatus according to the first embodiment, and the processing.

Steps S31 to S37 are the same as steps S121 to S131 in FIG. In step S38, the minimum transfer pulse Sp is derived, and in step S40, the transfer pulse effective range Vp is derived. In steps S39 and S40, the CPU 4 transfers the minimum transfer pulse Sp and the transfer pulse effective range Vp to the head control ASIC 3, and each value is stored in a register (not shown) in the head control ASIC 3. In step S 42, a one-dimensional γ table is generated based on the stored minimum transfer pulse Sp and transfer pulse effective range Vp, and written in the SDRAM 10. The processing from step S43 to step S48 is the same as the processing from step S131 to step S136 in FIG.
In step S49, error diffusion processing is performed. FIG. 4 is a block diagram showing in detail the configuration for performing step S49.
In FIG. 4, the data output from step S48 for edge enhancement is input image data, and the output for the dot data generation S50 is output image data.

  First, the quantizer 42 quantizes the image data input to the quantizer 42 for each pixel. The subtracter 43 obtains a difference between the input value and the output value in the quantizer 42 and derives a quantization error. The quantization correction unit 41 adds a correction value to the quantization result by the quantizer 42 and controls so that the output value from the quantizer does not become the minimum transfer pulse Sp or less. The quantization correction unit 41 holds the value of the minimum transfer pulse Sp obtained in step S38 of FIG. 3, and determines a correction value according to the minimum transfer pulse Sp. Thereafter, the quantization error is diffused to the surrounding pixels by the diffusion filter 44. The diffusion coefficient used in the diffusion filter 44 is read from the coefficient LUT 45.

Since the correlation between each diffusion coefficient and the pixel of interest is the same as that in FIG. In the coefficient LUT 45, the coefficients C1 to C4 are held in the diffusion coefficient group Cb [i] as shown in FIG. i represents a pulse value, and unlike the conventional method, a coefficient is held corresponding to the pulse value. The diffusion coefficient group Cb is stored as a diffusion coefficient group Cn for each temperature as shown in FIGS. 8 and 9, and is held for each environmental temperature and head temperature. Therefore, an optimum diffusion coefficient filter is selected from the coefficient LUT 45 in accordance with the minimum transfer pulse Sp, transfer pulse effective range Vp, environmental temperature, and head temperature held in a register (not shown) in the head control ASIC. The adder 46 adds the diffused error to the input image data and performs error diffusion. This process is performed for each pixel.
By selecting a diffusion coefficient filter corresponding to the environment and the temperature condition of the recording head, the minimum transfer pulse Sp, and the transfer pulse effective range Vp, it is possible to obtain a better error diffusion effect.

Finally, in step S139, the CPU 4 issues an energization request to the head control ASIC 3. In step S140, energization of the recording head is started, and the CPU starts processing of the M surface to be processed next in step S141.
Since the processing from step S121 to step S140 is performed on the Y, M, C surface and the protective film surface, the processing is repeated four times for one printed matter.

  As described above, according to this embodiment, in the sublimation type image forming apparatus, even if the input image data is quantized by the error diffusion method, it can be output in a stable region for printing. As a result, it is possible to reduce factors that significantly impair the image quality, such as untransferred and fading that are likely to occur in unstable regions.

(Example 2)
In the first embodiment, by correcting the quantization result output from the quantizer 42 in accordance with the environment and the temperature condition of the recording head, output to a region other than a region where the print output can be stably prevented is prevented. . In the second embodiment, an example will be described in which the image data after being quantized by the error diffusion method is clipped to prevent print output in an unstable region. Detailed descriptions of configurations similar to those in the above-described embodiment and examples are omitted. Hereinafter, one embodiment will be described in detail with reference to FIG.
The quantizer 42, subtractor 43, diffusion filter 44, and coefficient LUT 45 in FIG. 5 are the same as those shown in FIG.
The second embodiment is the same as the first embodiment except for the clip processing unit 51 in FIG.

  The clip processing unit 51 performs clip processing so that the value after quantization in each pixel is larger than the minimum transfer pulse Sp and smaller than the sum of the minimum transfer pulse Sp and the transfer pulse effective range Vp. The clip processor 51 receives the values of the minimum transfer pulse Sp and the transfer pulse effective range Vp obtained in steps S38 and S40 in FIG. By controlling so that the output value from the quantizer 42 does not fall below the minimum transfer pulse Sp, it is possible to prevent printing in an unstable region for printing, and to obtain a printed matter with good image quality. .

(Example 3)
In the third embodiment, an example in which normalization processing is performed on data quantized by the error diffusion method will be described. Detailed description of the same configuration as that of the above-described embodiment is omitted.

  Hereinafter, one embodiment of the present invention will be described in detail with reference to FIG.

The quantizer 42, the subtractor 43, the diffusion filter 44, and the coefficient LUT 45 in FIG. 6 are the same as those shown in FIG. The third embodiment is the same as the first embodiment except for the normalization processing unit 61 in FIG.
The normalization processing unit 6 performs normalization processing so that the value after quantization in each pixel is larger than the minimum transfer pulse Sp and smaller than the sum of the minimum transfer pulse Sp and the transfer pulse effective range Vp. The normalization processing unit 66 receives the values of the minimum transfer pulse Sp and the transfer pulse effective range Vp obtained in steps S38 and S40 in FIG. By controlling by the normalization process so that the output value from the quantizer 42 does not fall below the minimum transfer pulse Sp, printing in an unstable region for printing can be prevented, and a printed matter with good image quality can be obtained. Can be obtained.

[Other Examples]
In the above-described embodiment, the lower limit value of the area where printing can be performed stably is set according to the head temperature and the environmental temperature, but it is not always necessary to consider both, and only the head temperature may be used. In addition, the lower limit value and the range of the area where printing can be performed stably are set, but the same applies to a configuration where the lower limit value and the upper limit value are set.
The present invention also provides a system or apparatus with a storage medium storing software program codes for realizing the functions of the above-described embodiments (for example, the functions shown in the flowcharts of FIGS. 3 and 12). realizable. In this case, the function of the above-described embodiment is realized by the computer (or CPU or MPU) of the system or apparatus reading and executing the program code stored in the storage medium so that the computer can read it.

Claims (16)

In a sublimation type image forming apparatus that prints using a recording head,
Head temperature measuring means for measuring the temperature of the recording head;
Range setting means for setting a range of image data that can be stably printed by the image forming apparatus according to the temperature of the recording head;
Error diffusion processing means for quantizing the input image data by an error diffusion method;
Based on the range, it has a control means for controlling the result of the error diffusion processing means,
The error diffusion processing means selects a diffusion coefficient used for the error diffusion method according to the temperature of the recording head, and performs quantization by the error diffusion method on the input image data using the selected diffusion coefficient. An image forming apparatus that executes the image forming apparatus.   The image forming apparatus according to claim 1, wherein the control unit performs control so that a result of the error diffusion processing unit does not fall below a lower limit value of the range. Furthermore, the image forming apparatus has a lower limit setting unit that sets a lower limit of image data that can be stably printed according to the temperature of the recording head,
The image forming apparatus according to claim 1, wherein the control unit performs control based on the lower limit value and the range. Furthermore, an environmental temperature measuring means for measuring the environmental temperature ,
Holding means for holding a table indicating a range of image data that can be stably printed by the image forming apparatus according to the temperature of the recording head and the environmental temperature ;
The range setting means refers to the table of the holding means, and determines the range according to the temperature of the recording head obtained from the head temperature measuring means and the environmental temperature obtained from the environmental temperature measuring means. The image forming apparatus according to claim 1, wherein the image forming apparatus is set. Γ correction means for outputting a result of changing a gradation value indicating image data for each color component that can be printed by the image forming apparatus according to the range into a pulse value;
The error diffusion processing unit uses the image data based on the output result from the γ correction unit as input image data, and further, for each pixel value constituting the input image data, among the diffusion coefficients selected according to the temperature of the recording head. The image forming apparatus according to claim 3, wherein a diffusion coefficient is selected. The image forming apparatus according to claim 1, wherein the control unit includes correcting a result of the error diffusion processing unit.   The image forming apparatus according to claim 1, wherein the control unit performs a clipping process on a result obtained by the error diffusion processing unit.   The image forming apparatus according to claim 1, wherein the control unit normalizes a result obtained by the error diffusion processing unit. The error diffusion processing means quantizes a pixel value of a target pixel constituting the input image data, corrects a quantization result obtained by the quantization using a correction amount, and outputs the result as the error diffusion processing result. ,
Further, a difference between the pixel value of the target pixel and the result of the error diffusion process is calculated as a quantization error, and the quantization error is diffused to the pixels in the vicinity of the target pixel by using the diffusion coefficient. The image forming apparatus according to claim 1, wherein pixel values of neighboring pixels are updated. The image forming apparatus according to claim 9, wherein the control unit sets the correction amount based on the range. In an image forming method by a sublimation type image forming apparatus for printing using a recording head,
A head temperature measuring step for measuring the temperature of the recording head;
A range setting step for setting a range of image data that can be stably printed by the image forming apparatus according to the temperature of the recording head;
An error diffusion process for quantizing the input image data by an error diffusion method;
A control step of controlling a result of the error diffusion processing step based on the range, and
The error diffusion processing step selects a diffusion coefficient used in the error diffusion method according to the temperature of the recording head, and performs quantization by the error diffusion method on the input image data using the selected diffusion coefficient. An image forming method which is executed . A computer program for controlling a computer device to function as each unit of the image forming apparatus according to any one of claims 1 to 10 . In a sublimation type image forming apparatus,
Environmental measuring means for measuring environmental temperature;
Range setting means for setting a range of image data that can be stably printed by the image forming apparatus according to the environmental temperature;
Error diffusion processing means for quantizing the input image data by an error diffusion method;
Control means for controlling the result of the error diffusion processing means based on the range;
Have
The error diffusion processing means selects a diffusion coefficient to be used for the error diffusion method according to the temperature of the environment, and executes quantization by the error diffusion method on the input image data using the selected diffusion coefficient. An image forming apparatus. An image processing apparatus for a sublimation type image forming apparatus,
Range setting means for setting a range of pulse values that the image forming apparatus can stably print;
  A diffusion coefficient setting means for setting a diffusion coefficient used in the error diffusion method based on the range;
An image processing apparatus comprising: error diffusion processing means for performing quantization on input image data by an error diffusion method using the diffusion coefficient set by the diffusion coefficient setting means. In an image forming method using a sublimation type image forming apparatus,
An environmental measurement process for measuring environmental temperature;
A range setting step for setting a range of image data that can be stably printed by the image forming apparatus according to the environmental temperature;
An error diffusion process for quantizing the input image data by an error diffusion method;
A control step for controlling a result in the error diffusion processing step based on the range;
The error diffusion processing step selects a diffusion coefficient used for the error diffusion method according to the temperature of the environment, and executes quantization by the error diffusion method on the input image data using the selected diffusion coefficient. An image forming method. An image processing method for a sublimation type image forming apparatus,
A range setting step for setting a range of pulse values that can be stably printed by the image forming apparatus;
A diffusion coefficient setting step for setting a diffusion coefficient used in the error diffusion method according to the range,
An image processing method comprising: an error diffusion processing step of quantizing input image data by an error diffusion method using the diffusion coefficient set in the diffusion coefficient setting step.

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